A Study on Fatigue Failure of Bicrystals by means of in site SEM-ECP Observation

众所周知，软金属疲劳裂纹在持久滑移带（PSB）处形核。然而，PSB的特征与疲劳性能之间的关系并不清楚。本研究利用电子沟道花样（ECP）方法探讨了铜单晶和双晶的拉伸变形和疲劳行为.采用拉-压疲劳试验方法研究了预拉伸条件下铜单晶的疲劳行为。(1)结果表明，预应变提高了疲劳寿命。(2)预应变导致光合细菌的破碎。(3)预应变显著降低了疲劳裂纹的形核和扩展速率。(4)只有在疲劳试样中观察到的特征位错结构的形成受到预应变的干扰。用选区电子沟道花样（SACP）方法研究了晶界对双晶形变行为的影响。(5)该方法可用于评价晶界附近的塑性变形行为。(6)晶界影响区（GBAZ）强烈依赖于晶界处的应变不相容性。(7)GBAZ随着拉伸变形量的增加而增加。

It has been well known that in soft metals fatigue cracks nucleate at persistent slip band (PSB). However, the relation between the feature of PSB and fatigue behavior is not so clear. In this study, electron channeling pattern (ECP) method was applied to discuss about both tensile deformation and fatigue behavior of Cu single crystals and bicrystals.1. Fatigue behavior of Cu single crystals subjected to tensile pre-straining was studied by means of push-pull fatigue test.(1) It is found that pre-straining caused the increase of fatigue life.(2) Pre-straining caused the fragmentation of PSB.(3) Both nucleation and growth rate of fatigue cracks was prominently reduced by pre-straining.(4) The formation of characteristic dislocation structure observed only in fatigued specimens was disturbed by pre-straining.2. The effect of grain boundary on deformation behavior of bicrystals was studied by means of selected area electron channeling pattern (SACP) method.(5) Plastic deformation behavior near the grain boundary could be evaluated by this method.(6) Grain boundary affected zone (GBAZ) depended strongly on the strain incompatibility at the grain boundary.(7) GBAZ increased with the increase of tensile deformation.